High-efficiency pv panel with conductive backsheet

ABSTRACT

One embodiment of the invention can provide a solar panel, which can include a cover, a backsheet, and a plurality of solar cell strings. The backsheet can include a first insulation layer, a second insulation layer, and a conductive interlayer positioned between the first insulation layer and the second insulation layer. The solar cell strings can be positioned between the cover and the first insulation layer of the backsheet. The first insulation layer can include a plurality of vias, and the conductive interlayer can be patterned according to locations of the vias, thereby facilitating electrical interconnections among the solar cell strings.

CROSS-REFERENCE TO OTHER APPLICATIONS

This claims the benefit of U.S. Provisional Patent Application No. 62/088,509, Attorney Docket Number P103-1PUS, entitled “SYSTEM, METHOD, AND APPARATUS FOR AUTOMATIC MANUFACTURING OF SOLAR PANELS,” filed Dec. 5, 2014; and U.S. Provisional Patent Application No. 62/143,694, Attorney Docket Number P103-2PUS, entitled “SYSTEMS AND METHODS FOR PRECISION AUTOMATION OF MANUFACTURING SOLAR PANELS,” filed Apr. 6, 2015; the disclosures of which are incorporated herein by reference in their entirety for all purposes.

This is also related to U.S. patent application Ser. No. 14/563,867, Attorney Docket Number P67-3NUS, entitled “HIGH EFFICIENCY SOLAR PANEL,” filed Dec. 8, 2014; and U.S. patent application Ser. No. 14/510,008, Attorney Docket Number P67-2NUS, entitled “MODULE FABRICATION OF SOLAR CELLS WITH LOW RESISTIVITY ELECTRODES,” filed Oct. 8, 2014; the disclosures of which are incorporated herein by reference in their entirety for all purposes.

FIELD OF THE INVENTION

This is generally related to solar panels. More specifically, this is related to a solar panel that achieves inter-cell electrical connections via a conductive backsheet.

DEFINITIONS

“Solar cell” or “cell” is a photovoltaic structure capable of converting light into electricity. A cell may have any size and any shape, and may be created from a variety of materials. For example, a solar cell may be a photovoltaic structure fabricated on a silicon wafer or one or more thin films on a substrate material (e.g., glass, plastic, or any other material capable of supporting the photovoltaic structure), or a combination thereof.

A “solar cell strip,” “photovoltaic strip,” or “strip” is a portion or segment of a photovoltaic structure, such as a solar cell. A photovoltaic structure may be divided into a number of strips. A strip may have any shape and any size. The width and length of a strip may be the same or different from each other. Strips may be formed by further dividing a previously divided strip.

A “cascade” is a physical arrangement of solar cells or strips that are electrically coupled via electrodes on or near their edges. There are many ways to physically connect adjacent photovoltaic structures. One way is to physically overlap them at or near the edges (e.g., one edge on the positive side and another edge on the negative side) of adjacent structures. This overlapping process is sometimes referred to as “shingling.” Two or more cascading photovoltaic structures or strips can be referred to as a “cascaded string,” or more simply as a string.

“Finger lines,” “finger electrodes,” and “fingers” refer to elongated, electrically conductive (e.g., metallic) electrodes of a photovoltaic structure for collecting carriers.

A “busbar,” “bus line,” or “bus electrode” refers to an elongated, electrically conductive (e.g., metallic) electrode of a photovoltaic structure for aggregating current collected by two or more finger lines. A busbar is usually wider than a finger line, and can be deposited or otherwise positioned anywhere on or within the photovoltaic structure. A single photovoltaic structure may have one or more busbars.

A “photovoltaic structure” can refer to a solar cell, a segment, or solar cell strip. A photovoltaic structure is not limited to a device fabricated by a particular method. For example, a photovoltaic structure can be a crystalline silicon-based solar cell, a thin film solar cell, an amorphous silicon-based solar cell, a poly-crystalline silicon-based solar cell, or a strip thereof.

BACKGROUND

Advances in photovoltaic technology, which are used to make solar panels, have helped solar energy gain mass appeal among those wishing to reduce their carbon footprint and decrease their monthly energy costs. However, the panels are typically fabricated manually, which is a time-consuming and error-prone process that makes it costly to mass-produce reliable solar panels.

Solar panels typically include one or more strings of complete photovoltaic structures. Adjacent photovoltaic structures in a string may overlap one another in a cascading arrangement. For example, continuous strings of photovoltaic structures that form a solar panel are described in U.S. patent application Ser. No. 14/510,008, filed Oct. 8, 2014 and entitled “Module Fabrication of Solar Cells with Low Resistivity Electrodes,” the disclosure of which is incorporated herein by reference in its entirety. Producing solar panels with a cascaded cell arrangement can reduce the resistance due to inter-connections between the cells, and can increase the number of photovoltaic structures that can fit into a solar panel.

Moreover, it has been shown that solar panels based on strings of strips cascaded in parallel, which are created by dividing complete photovoltaic structures, provide several advantages, including but not limited to: reduced shading, enablement of bifacial operation, and reduced internal resistance. Detailed descriptions of a solar panel based on cascaded strips can be found in U.S. patent application Ser. No. 14/563,867, entitled “HIGH EFFICIENCY SOLAR PANEL,” filed Dec. 8, 2014, the disclosures of which is incorporated herein by reference in its entirety for all purposes. Conventional inter-string connections, including both serial and parallel connections, can involve cumbersome wirings, which often not only complicates the panel manufacturing process but also leads to extra shading.

In addition to interconnecting strings of photovoltaic structures, forming a solar panel also involves connecting each string or portion of the strings to bypass diodes. The bypass diodes can be used to prevent currents flowing from good photovoltaic structures (photovoltaic structures are well-exposed to sunlight and in normal working condition) to bad photovoltaic structures (photovoltaic structures that are burning out or partially shaded) by providing a current path around the bad cells. Ideally, there would be one bypass diode connected to each photovoltaic structure, but electrical connections can be too complicated and expensive. In most cases, one bypass diode can be used to protect a group of serially connected strips, which can be a string or a portion of a string. However, connecting strings or cascaded strips to bypass diodes can be challenging because the strings do not have exposed busbars, except at the very end of the string. In other words, it can be difficult to access a photovoltaic structure that is in the middle of a string.

SUMMARY

One embodiment of the invention can provide a solar panel, which can include a cover, a backsheet, and a plurality of solar cell strings. The backsheet can include a first insulation layer, a second insulation layer, and a conductive interlayer positioned between the first insulation layer and the second insulation layer. The solar cell strings can be positioned between the cover and the first insulation layer of the backsheet. The first insulation layer can include a plurality of vias, and the conductive interlayer can be patterned according to locations of the vias, thereby facilitating electrical interconnections among the solar cell strings.

In a variation on the embodiment, the first insulation layer can include polyethylene terephthalate (PET), fluoropolymer, polyvinyl fluoride (PVF), polyamide, or any combination thereof. The conductive interlayer can include Al, Cu, graphite, conductive polymer, or any combination thereof.

In a variation on the embodiment, a respective via can be filled with conductive paste to facilitate electrical coupling between contact pad located on a corresponding solar cell string and the conductive interlayer and/or mechanical bonding between a contact pad located on a corresponding solar cell string and the conductive interlayer.

In a variation on the embodiment, a respective solar cell string can include a plurality of cascaded photovoltaic structures.

In a variation on the embodiment, the solar panel can further include a plurality of bypass diodes, wherein a respective bypass diode can be coupled to a photovoltaic structure through the conductive interlayer.

In a variation on the embodiment, a conductive path between a first solar cell string and a second solar cell string can include: a first contact pad of the first solar cell string, a first set of vias within the first insulation layer, wherein the first set of vias can be filled with conductive paste and positioned beneath the first contact pad, a second contact pad of the second solar cell string, a second set of vias within the first insulation layer, wherein the second set of vias can be filled with conductive paste and positioned beneath the second contact pad, and a continuous portion of the conductive interlayer that can be in contact with both the first and second sets of vias.

In a variation on the embodiment, the second insulation layer can include a plurality of vias to electrically couple the interconnected solar cell strings to a junction box.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A shows an exemplary conductive grid pattern on the front surface of a photovoltaic structure.

FIG. 1B shows an exemplary conductive grid pattern on the back surface of a photovoltaic structure.

FIG. 2A shows a string of strips stacked in a cascaded pattern.

FIG. 2B shows the side-view of the string of the cascaded strips.

FIG. 3 shows the structure of an exemplary backsheet with a conductive interlayer.

FIG. 4A shows exemplary electrical coupling between a string and the conductive interlayer in the backsheet, according to an embodiment of the invention.

FIG. 4B shows a cross-sectional view of a string sandwiched between both covers of a solar panel, according to an embodiment of the invention.

FIG. 5A shows a cross-sectional view of two strings connected in series, according to an embodiment of the invention.

FIG. 5B shows the top view of two strings connected in series, according to an embodiment of the invention.

FIG. 6A shows a cross-sectional view of two strings connected in parallel, according to an embodiment of the invention.

FIG. 6B shows the top view of four strings connected in parallel, according to an embodiment of the invention.

FIG. 7A shows the back side of a string comprising cascaded strip, according to an embodiment of the invention.

FIG. 7B shows the back side of a string comprising cascaded strip, according to an embodiment of the invention.

FIG. 8A shows a cross-sectional view of a string mechanically bonded to the backsheet, according to an embodiment of the invention.

FIG. 8B shows the top view of a string mechanically bonded to the backsheet, according to an embodiment of the invention.

FIG. 9A shows the inter-string connections and the bypass protection strategy of a solar panel, according to an embodiment of the invention.

FIG. 9B shows the inter-string connections and the bypass protection strategy of a solar panel, according to an embodiment of the invention.

FIG. 10 shows the flowchart of manufacturing a solar panel, according to an embodiment of the invention.

In the figures, like reference numerals refer to the same figure elements.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

Overview

Embodiments of the invention provide a solar module that includes a conductive backsheet used for inter-cell electrical coupling. More specifically, the conductive backsheet can include a conductive (Cu or Al) middle layer sandwiched between multiple insulating layers. At the cell-facing side of the backsheet, vias can be formed by removing the insulating layers to expose the underneath conductive interlayer at selected locations. Conductive adhesive can fill the vias, thus enabling formations of conductive paths between the photovoltaic structure surface and the backsheet. To achieve inter-string electrical connections and connections to bypass diodes, the conductive middle layer can be patterned according to the solar panel layout design (including how the strings are placed and interconnected and what type of bypass protection strategy is used).

Solar Panel Based on Cascaded Strips

As described in U.S. patent application Ser. No. 14/563,867, a solar panel can have multiple (such as 3) strings, each string including cascaded strips, connected in parallel. Such a multiple-parallel-string panel configuration can provide the same output voltage with a reduced internal resistance. In general, a cell can be divided into a number of (e.g., n) strips, and a panel can contain a number of strings (the number of strings can be the same as or different from number of strips in the cell). If a string has the same number of strips as the number of regular photovoltaic structures in a conventional single-string panel, the string can output approximately the same voltage as a conventional panel. Multiple strings can then be connected in parallel to form a panel. If the number of strings in a panel is the same as the number of strips in the cell, the solar panel can output roughly the same current as a conventional panel. On the other hand, the panel's total internal resistance can be a fraction (e.g., 1/n) of the resistance of a string. Therefore, in general, the greater n is, the lower the total internal resistance of the panel is, and the more power one can extract from the panel. However, a tradeoff is that as n increases, the number of connections required to inter-connect the strings also increases, which increases the amount of contact resistance. Also, the greater n is, the more strips a single cell needs to be divided into, which increases the associated production cost and decreases overall reliability due to the larger number of strips used in a single panel.

Another consideration in determining n is the contact resistance between the electrode and the photovoltaic structure on which the electrode is formed. The greater this contact resistance is, the greater n might need to be to reduce effectively the panel's overall internal resistance. Hence, for a particular type of electrode, different values of n might be needed to attain sufficient benefit in reduced total panel internal resistance to offset the increased production cost and reduced reliability. For example, conventional silver-paste or aluminum based electrode may require n to be greater than 4, because process of screen printing and firing silver paste onto a cell does not produce ideal resistance between the electrode and underlying photovoltaic structure. In some embodiments of the present invention, the electrodes, including both the busbars and finger lines, can be fabricated using a combination of physical vapor deposition (PVD) and electroplating of copper as an electrode material. The resulting copper electrode can exhibit lower resistance than an aluminum or screen-printed-silver-paste electrode. Consequently, a smaller n can be used to attain the benefit of reduced panel internal resistance. In some embodiments, n is selected to be three, which is less than the n value generally needed for cells with silver-paste electrodes or other types of electrodes. Correspondingly, two grooves can be scribed on a single cell to allow the cell to be divided to three strips.

In addition to lower contact resistance, electro-plated copper electrodes can also offer better tolerance to micro cracks, which may occur during a cleaving process. Such micro cracks might adversely impact silver-paste-electrode cells. Plated-copper electrode, on the other hand, can preserve the conductivity across the cell surface even if there are micro cracks in the photovoltaic structure. The copper electrode's higher tolerance for micro cracks allows one to use thinner silicon wafers to manufacture cells. As a result, the grooves to be scribed on a cell can be shallower than the grooves scribed on a thicker wafer, which in turn helps increase the throughput of the scribing process. More details on using copper plating to form a low-resistance electrode on a photovoltaic structure are provided in U.S. patent application Ser. No. 13/220,532, entitled “SOLAR CELL WITH ELECTROPLATED GRID,” filed Aug. 29, 2011, the disclosure of which is incorporated herein by reference in its entirety.

FIG. 1A shows an exemplary grid pattern on the front surface of a photovoltaic structure, according to one embodiment of the present invention. In the example shown in FIG. 1A, grid 102 includes three sub-grids, such as sub-grid 104. This three sub-grid configuration allows the photovoltaic structure to be divided into three strips. To enable cascading, each sub-grid needs to have an edge busbar, which can be located either at or near the edge. In the example shown in FIG. 1A, each sub-grid includes an edge busbar (“edge” here refers to the edge of a respective strip) running along the longer edge of the corresponding strip and a plurality of parallel finger lines running in a direction parallel to the shorter edge of the strip. For example, sub-grid 104 can include edge busbar 106, and a plurality of finger lines, such as finger lines 108 and 110. To facilitate the subsequent laser-assisted scribe-and-cleave process, a predefined blank space (i.e., space not covered by electrodes) is inserted between the adjacent sub-grids. For example, blank space 112 is defined to separate sub-grid 104 from its adjacent sub-grid. In some embodiments, the width of the blank space, such as blank space 112, can be between 0.1 mm and 5 mm, preferably between 0.5 mm and 2 mm. There is a tradeoff between a wider space that leads to more tolerant scribing operation and a narrower space that leads to more effective current collection. In a further embodiment, the width of such a blank space can be approximately 1 mm.

FIG. 1B shows an exemplary grid pattern on the back surface of a photovoltaic structure, according to one embodiment of the invention. In the example shown in FIG. 1B, back grid 120 can include three sub-grids, such as sub-grid 122. To enable cascaded and bifacial operation, the back sub-grid may correspond to the front sub-grid. More specifically, the back edge busbar needs to be located at the opposite edge of the frontside edge busbar. In the examples shown in FIGS. 1A and 1B, the front and back sub-grids have similar patterns except that the front and back edge busbars are located adjacent to opposite edges of the strip. In addition, locations of the blank spaces in back conductive grid 120 correspond to locations of the blank spaces in front conductive grid 102, such that the grid lines do not interfere with the subsequent scribe-and-cleave process. In practice, the finger line patterns on the front and back side of the photovoltaic structure may be the same or different.

In the examples shown in FIGS. 1A and 1B, the finger line patterns can include continuous, non-broken loops. For example, as shown in FIG. 1A, finger lines 108 and 110 both include connected loops with rounded corners. This type of “looped” finger line pattern can reduce the likelihood of the finger lines from peeling away from the photovoltaic structure after a long period of usage. Optionally, the sections where parallel lines are joined can be wider than the rest of the finger lines to provide more durability and prevent peeling. Patterns other than the one shown in FIGS. 1A and 1B, such as un-looped straight lines or loops with different shapes, are also possible.

To form a cascaded string, cells or strips (e.g., as a result of a scribing-and-cleaving process applied to a regular square-shaped cell) can be cascaded with their edges overlapped. FIG. 2A shows a string of cascaded strips, according to an embodiment of the invention. In FIG. 2A, strips 202, 204, and 206 are stacked in such a way that strip 206 partially overlaps adjacent strip 204, which also partially overlaps (on an opposite edge) strip 202. Such a string of strips forms a pattern that is similar to roof shingles. Each strip includes top and bottom edge busbars located at opposite edges of the top and bottom surfaces, respectively. Strips 202 and 204 are coupled to each other via an edge busbar 208 located at the top surface of strip 202 and an edge busbar 210 located at the bottom surface of strip 204. To establish electrical coupling, strips 202 and 204 are placed in such a way that bottom edge busbar 210 is placed on top of and in direct contact with top edge busbar 208.

FIG. 2B shows a side view of the string of cascaded strips, according to one embodiment of the invention. In the example shown in FIGS. 2A and 2B, the strips can be part of a 6-inch square-shaped photovoltaic structure, with each strip having a dimension of approximately 2 inches by 6 inches. To reduce shading, the overlapping between adjacent strips should be kept as small as possible. In some embodiments, the single busbars (both at the top and the bottom surfaces) are placed at the very edge of the strip (as shown in FIGS. 2A and 2B). The same cascaded pattern can extend along an entire row of strips to form a serially connected string.

From FIGS. 2A and 2B one can see that, other than at both ends of a string, all busbars are sandwiched between the overlapped strips. This no-busbar configuration reduces shading. However, hiding the busbars makes it difficult to electrically access the photovoltaic structures, especially the strips that are in the middle of a string. In addition, although a string can be connected to a different string via busbars at either ends of the string, connecting the strings may sometimes require flipping over a string of cascaded strips, which is not an easy task considering that a string may include tens of cascaded strips and the strips are made of fragile Si wafers.

Electrical Interconnection Based on a Conductive Backsheet

The manufacture of a solar panel typically involves encapsulating photovoltaic structures between two layers of protective material, which are the front and back covers. The light-facing side of the panel often includes a glass cover, and the side facing away from light often includes a non-transparent cover, known as the backsheet. Typical backsheets for solar panels are made of polyvinyl fluoride (PVF) or polyethylene terephthalate (PET) films, which are electrical insulating. Alternatively, a solar panel backsheet may include a conductive interlayer sandwiched between layers of insulating materials. The conductive interlayer can include a conductive interlayer, which can include metallic materials (e.g., Al, Cu, or their alloy) or non-metallic conductive materials (e.g., graphite or conductive polymer).

FIG. 3 shows the structure of an exemplary backsheet with a conductive interlayer. In FIG. 3, backsheet 300 includes a plurality of layers, including primer layer 302 facing the photovoltaic structures, electrical-grade PET layer 306, adhesive layer 304 positioned between primer layer 302 and electrical-grade PET layer 306, conductive interlayer 310, adhesive layer 308 positioned between conductive interlayer 310 and electrical-grade PET layer 306, PET layer 314 that is hydrolysis resistant and UV stable, and adhesive layer 312 positioned between conductive interlayer 310 and hydrolysis-resistant PET layer 314. The outer PET layers 302 and 314 provide excellent electrical insulation, which is essential to protect the photovoltaic structures from being exposed to external voltage. In addition to PET, other insulating materials, such as PVF, Polyamide, and Tedlar® (registered trademark of E. I. du Pont de Nemours and Company of Wilmington, Del.), may also be used as outer layers that encapsulate the conductive interlayer.

The usage of a backsheet having a conductive interlayer is originally motivated by the need of a moisture barrier inside a solar panel. However, the existence of a conductive interlayer inside the backsheet can also provide the possibility of establishing electrical paths through the backsheet. More specifically, when two solar strings need to be coupled electrically, one may electrically couple an exposed busbar of one string to a point on the conductive interlayer and couple an exposed busbar of the other string to another point on the conductive interlayer. If a continuous layer of conductive material exists between these two points, these two strings can be electrically coupled. This way, there is no need for additional tabbing wires between the two strings, which not only saves material cost but also simplifies the panel fabrication process.

Electrically coupling between a string and a conductive interlayer of the backsheet requires a way to bypass the insulating PET layer positioned between the string and the conductive interlayer. In some embodiments, vias (or through holes) can be created in the insulating PET layer, and conductive paste can be used to fill these vias to establish a conductive path between the busbar of an edge strip of the string and the conductive interlayer.

FIG. 4A shows exemplary electrical coupling between a string of photovoltaic structures and the conductive interlayer in the backsheet, according to an embodiment of the invention. In FIG. 4A, backsheet 410 can include top insulation layer 412, conductive interlayer 414, and bottom insulation layer 416. A cascaded string 402 can include edge busbar 404 facing backsheet 410. Other busbars within string 402 (with the exception of a busbar at the other edge, not shown in FIG. 4A) are sandwiched between the cascaded strip edges, and are not electrically accessible. For simplicity, the individual photovoltaic structures or strips in string 402 are not drawn in detail. One can refer to FIGS. 2A and 2B for details about how the strips are cascaded.

Establishing electrical coupling between string 402 and conductive interlayer 414 can involve creating a conductive path between edge busbar 404 and conductive interlayer 414. In the example shown in FIG. 4A, such a conductive path can be formed by creating via 418 (or through hole 418) within top insulation layer 412 at a location that is directly beneath busbar 404, and by filling via 418 with a conductive material. The conductive material is then in direct contact with both busbar 404 and conductive interlayer 414, thus forming a conductive path between them.

Via 418 can be formed by selective etching top insulation layer 412. The conductive material used to fill via 418 can include a conductive paste (or adhesive), which can not only provide conductivity but can also enhance the bonding between string 402 and backsheet 410. The conductive adhesive or paste can have various forms. In one embodiment, the conductive adhesive can include a conductive metallic core surrounded by resin. When the conductive paste fills via 418, the metallic core can establish electrical connections, while the resin that surrounds the metallic core can function as an adhesive. In another embodiment, the conductive paste may be in the form of resin that includes a number of suspended conductive particles, such as Ag or Cu particles. These conductive particles may be coated with a protection layer that evaporates when the paste is thermally cured, thereby resulting in electrical conductivity among the conductive particles suspended inside the resin. The volume fraction of the conductive particles can be approximately between 50 and 90%

Also shown in FIG. 4A is sealant layer 420, which when thermally cured can seal the strings between the covers. Sealant layer 420 can be formed using various materials, such as ethylene-vinyl acetate (EVA), acrylic, polycarbonate, polyolefin, and thermal plastic. In some embodiments, sealant layer 420 may be part of backsheet 410.

FIG. 4B shows a cross-sectional view of a string sandwiched between both covers of a solar panel, according to an embodiment of the invention. In FIG. 4B, cascaded string 450 can be sandwiched between glass cover 460 and backsheet 440, and can be also embedded in sealant layer 470. Backsheet 440 can include top insulation layer 442, conductive interlayer 444, and bottom insulation layer 446. Cascaded string 450 can include edge busbars 452 and 454 that are on opposite (top and bottom) sides of the string, and conductive tab 456. In some embodiments, conductive tab 456 can be “L” shaped, as shown in FIG. 4B, which enables electrical access to busbar 454 from the opposite side of cascaded string 450. In further embodiments, conductive tab 456 may include a conductive core wrapped with a layer of insulating material. One end of the conductive core electrically couples to busbar 454, and the other end of the conductive core can be used to electrically access busbar 454. Conductive tab 456 may have other shapes or forms, as long as it can enable electrical access to busbar 454 from a side of cascaded string 450 that is opposite to the side where busbar 454 is located. For example, conductive tab 456 can shaped as a rectangular prism or two-step stairs. In some embodiments, conductive tab 456 can include a conductive core partially wrapped with an EPE film layer, which is a multi-layer film consisting of Vinyl Acetrate resin (EVA) bonded to both sides of a Polyester film. More pacifically, other than the string-facing surface, the surface that faces away from the string and sidewalls of conductive tab 456 can be completely covered by the EPE film. The EPE film can be chosen to be black to ensure consistence in appearance of the tabbed solar string.

In the example shown in FIG. 4B, electrical accesses to both sides, thus both polarities, of cascaded string 450 can come from the bottom side (or the side facing backsheet 440) of cascaded string 450. This is important in enabling inter-string connections via backsheet 440. In other words, the introduction of conductive tabs can enable single-sided electrical connections at the string level. This is different from other rear contact photovoltaic structures, such as interdigitated back contact (IBC) solar cells, emitter warp through (EWT) solar cells, and metallization wrap through (MWT) solar cells. More specifically, IBC and EWT solar cells require formations of oppositely doped regions at the back side of the photovoltaic structures, and EWT and MWT solar cells require drilling holes through the photovoltaic structures. All these can lead to a much more complex manufacturing process. On the other hand, in embodiments of the invention, the current-collecting finger lines and busbars are on both sides of the photovoltaic structures, and access to the busbars can be achieved from the same side of the photovoltaic structures without the need to form oppositely doped regions on one side or drill holes through the photovoltaic structures.

In FIG. 4B, top insulation layer 442 includes vias 462 and 464, with via 462 beneath busbar 452 and via 464 beneath conductive tab 456. Both vias 462 and 464 are filled with conductive paste, meaning that both busbars 452 and 454 are electrically coupled to conductive interlayer 444. For any photovoltaic structure to operate normally, the two polarities (i.e., the two busbars on the opposite sides) cannot be shorted. To prevent shorting between busbars 452 and 454 through conductive interlayer 444, gap 448 can be created within conductive interlayer 444 to electrically insulate the conductive portion coupled to busbar 452 from the conductive portion coupled to busbar 454.

On the other hand, when two strings need to be electrically coupled, either in series or in parallel, a continuous portion of the conductive interlayer can serve as a bridge to create a conductive path between busbars of the two strings. FIG. 5A shows a cross-sectional view of two strings connected in series, according to an embodiment of the invention. In FIG. 5A, string 510 and string 520 are sandwiched between glass cover 570 and backsheet 550. More specifically, strings 510 and 520 are placed adjacent to each other, with bottom busbar 512 of string 510 adjacent to conductive tab 526 that is coupled to top busbar 524 of string 520. Backsheet 550 can include top insulation layer 552, conductive interlayer 554, and bottom insulation layer 556. Considering all strings may be oriented the same way, meaning that busbars of the same polarity of all strings are facing the same side (top or bottom) of the panel, connecting strings 510 and 520 in series can require establishing a conductive path between bottom busbar 512 of string 510 and top busbar 524 of string 520. To do so, vias 562 and 564 underneath bottom busbar 512 and conductive tab 526, respectively, can be created within top insulation layer 552, and can be filled with conductive paste. As a result, a conductive path, as indicated by double arrow 566, can be established via conductive interlayer 554. Gaps 572 and 574 within conductive interlayer 554 can ensure that this conductive path is isolated from other circuitry within conductive interlayer 554.

FIG. 5B shows the top view of two strings connected in series, according to an embodiment of the invention. For purposes of illustration, the different layers are overlaid on each other in a transparent manner, although they are not transparent in real life. The vertical sequence of the layers can be seen in FIG. 5A. For example, string 510 is drawn transparently to reveal bottom busbar 512 and via 562. The dotted background is conductive interlayer 554. Also shown in FIG. 5B are vias 562 and 564 filled with conductive paste. These vias are within the top insulation layer, which is not explicitly shown in FIG. 5B. The conductive paste filled in vias 562 and 564 can electrically couple busbar 512 and conductive tab 526 to conductive portion 568 carved out of conductive interlayer 554. From FIG. 5B, one can see that portion 568 is insulated from the rest of conductive interlayer 554 by a gap surrounding portion 568. Consequently, although conductive portion 568 can provide a conductive path between busbar 512 and conductive tab 526, such a conductive path does not lead to anywhere else, thus preventing possible shorting of the strings.

FIG. 6A shows a cross-sectional view of two strings connected in parallel, according to an embodiment of the invention. In FIG. 6A, string 610 and string 620 can be sandwiched between glass cover 670 and backsheet 650. Unlike what is shown in FIG. 5A, in FIG. 6A, strings 610 and 620 can be placed in such a way that bottom busbar 612 of string 610 is adjacent to bottom busbar 622 of string 620. Backsheet 650 can include top insulation layer 652, conductive interlayer 654, and bottom insulation layer 656. Because bottom busbars 612 and 622 are of the same polarity, the parallel connection of strings 610 and 620 can require establishing a conductive path between bottom busbar 612 of string 610 and bottom busbar 622 of string 620. Similarly, a conductive path needs to be established between top busbars 614 and 624.

Similar to what is shown in FIG. 5A, vias 662 and 664 underneath bottom busbars 612 and 622, respectively, can be created within top insulation layer 652, and can be filled with conductive paste. Through the conductive paste and conductive interlayer 654, a conductive path, as indicated by double arrow 666, can be established between bottom busbars 612 and 622. Gaps 672 and 674 within conductive interlayer 654 ensure that this conductive path is isolated from other circuitry within conductive interlayer 654. Similarly, a conductive path can be established between top busbars 614 and 624 through conductive tabs 616 and 626, vias 682 and 684 that are filled with conductive paste, and conductive interlayer 654.

In certain cases, the strings connected in parallel may be connected to a junction box located on the opposite side (the side facing away from the strings) of backsheet 650 to enable connections to other circuitries outside of the panel. In some embodiments, the electrical coupling between inter-connected strings and the junction box can also be achieved via the conductive interlayer in the backsheet. In the example shown in FIG. 6A, vias 676 and 678 are created within bottom insulation layer 656, and are filled with conductive paste, thus enabling electrical access from the outside of the panel to the strings. More specifically, via 676 enables electrical coupling to bottom busbars of the strings and via 678 enables electrical coupling to top busbars of the strings. As one can see from FIG. 6A, the pattern of conductive interlayer 654 can be designed in a way to allow vias 676 and 678 to be in close vicinity of each other, making it easier to establish connections to the junction box.

FIG. 6B shows the top view of four strings connected in parallel, according to an embodiment of the invention. For purposes of illustration, the different layers are overlaid on each other in a transparent manner, although they are not transparent. The vertical sequence of the layers can be seen in FIG. 6A.

In FIG. 6B, conductive interlayer 654 include portion 655 that is carved out and insulated from the rest of conductive interlayer 654. Carved out portion 655 can form an equal potential plane that electrically couples the bottom busbars of the four strings through conductive paste filled in strategically positioned vias, e.g., vias 662 and 664, which couple the bottom busbars of strings 610 and 620 to conductive portion 655. On the other hand, the remaining portion of conductive interlayer 654 can form a second equal potential plane that electrically couples the top busbars of the four strings. For example, conductive paste filled in vias 682 and 684 can couple the top busbars of strings 610 and 620 to the remaining portion of conductive interlayer 654. As a result, the four strings shown in FIG. 6B are connected in parallel with one polarity (the bottom busbars) coupled to carved out portion 655 and the other polarity (the top busbars) coupled to the remaining portion of conductive interlayer 654. Conductive paste filled in vias 676 and 678 within the bottom insulation layer can enable electrical access to the two polarities of the strings from the back side of the backsheet.

In the examples shown in FIGS. 5B and 6B, each busbar is coupled to the conductive interlayer through one via filled with conductive paste. In practice, multiple vias filled with conductive paste can be used to establish the conductive path to the conductive interlayer. Using multiple vias not only can reduce the series resistance, but also can strengthen the bonding between the string and the backsheet.

In addition to enabling inter-string connections, the conductive backsheet may also be used to provide electrical access to middle strips of a string. Accessing the middle strips can be important, especially if one wants to provide bypass protections at a higher granularity than an individual string. For example, to provide bypass protections to half of the strips within a string, one may need to connect a bypass diode in parallel to the half string; that is, electrically couple to a strip in the middle of the string. In some embodiments, some of the strips within a string can include specially designed “contact pads” (sometimes also called “landing pads”) to enable electrical access to a strip, even when such a strip is positioned in the middle of a cascaded string, as shown in FIGS. 7A and 7B.

FIG. 7A shows the back side of a string comprising cascaded strips, according to an embodiment of the invention. In the example shown in FIG. 7A, strip 702 can be positioned in the middle of string 700, and can include a number of exposed contact pads, such as contact pad 704. These contact pads can be part of the electrodes on strip 702, thus enabling electrical connections to strip 702. Similarly, FIG. 7B shows the back side of a string comprising cascaded strips, according to an embodiment of the invention. In the example shown in FIG. 7B, strip 712 can be positioned in the middle of string 710, and can include additional non-edge busbar 716. Non-edge busbar 716 is exposed and can have multiple widened areas, such as widened area 716. These widened areas can act as contact pads to enable electrical connections to strip 712. More specifically, the landing or contact pads, such as the ones shown in FIGS. 7A and 7B, allow a bypass diode to be used to protect a portion of the cascaded string. Detailed descriptions of the contact/landing pads can be found in co-pending U.S. patent application No. TBA, Attorney Docket Number P142-1NUS, entitled “PHOTOVOLTAIC ELECTRODE DESIGN WITH CONTACT PADS FOR CASCADED APPLICATION,” filed ______, 2015, the disclosure of which is incorporated herein by reference in its entirety for all purposes.

In addition to enabling the sub-string level bypass protection, these contact pads can also facilitate mechanical bonding between the string and the backsheet. FIG. 8A shows a cross-sectional view of a string mechanically bonded to the backsheet, according to an embodiment of the invention. In FIG. 8A, string 810 can be positioned between front cover 820 and backsheet 830. Backsheet 830 can include top insulation layer 832, conductive interlayer 834, and bottom insulation layer 836. Backsheet 830 may optionally include sealant layer 838. For simplicity, FIG. 8A only shows one additional busbar 812 located in the middle of string 810, and does not show the edge busbars.

To facilitate mechanical bonding between string 810 and backsheet 830, via 842 can be created in top insulation layer 832 underneath additional busbar 812. By filling via 842 with adhesives (which can include conductive paste or other insulating adhesives), one can mechanically bond string 810 to backsheet 830. More specifically, the adhesives bond string 810 to conductive interlayer 834. Since the adhesives most likely include conductive paste (to keep the paste application process consistent), to prevent undesired electrical coupling, portion 844 that is in contact with the conductive paste can be insulated from the rest of conductive interlayer 834 via gaps 846 and 848. As a result, adhesives within via 842 merely serve the purpose of establishing mechanical bonding, and do not provide any electrical coupling.

FIG. 8B shows the top view of a string mechanically bonded to the backsheet, according to an embodiment of the invention. For purposes of illustration, the different layers are overlaid on each other in a transparent manner, although they are not transparent. For example, string 810 is shown as transparent to reveal additional busbar 812. The vertical sequence of the layers can be seen in FIG. 8A. As shown in FIG. 8B, a number of vias, such as via 842, are created under additional busbar 812 of string 810. Adhesives, such as conductive paste, filled in these vias couple string 810 to portion 844 within conductive interlayer 834. Because portion 844 is segregated from other portions of conductive interlayer 834, no electrical coupling to additional busbar 812 can be established through portion 844. The examples shown in FIGS. 8A and 8B can also be applied to scenarios where the contact pads are widened areas of the edge busbars.

In the example shown in FIG. 6B, four strings are interconnected to each other through the conductive interlayer. In practice, a solar panel may include more inter-connected strings, and multiple bypass diodes can be used to bypass protect strings or portions of a string. FIG. 9A shows the inter-string connections and the bypass protection strategy of a solar panel, according to an embodiment of the invention.

In FIG. 9A, solar panel 900 includes a number of cascaded strings, such as strings 902 and 904. Each cascaded string can include a series of strips stacked in a cascaded manner. In most cases, the strips are orientated in such a way that they are connected in series (similar to the example shown in FIG. 5A). Multiple cascaded strings can also be connected in series to form a larger string, which can output a larger voltage than a single cascaded string. In the example shown in FIG. 9A, cascaded strings 902 and 904 and two other strings are connected in series to form larger string 912. The serial connection can be formed through portions of the conductive interlayer in the backsheet. For example, the negative polarity (as indicated by the “−” sign) of cascaded string 902 can be coupled to the positive polarity (as indicated by the “+” sign) of cascaded string 904 via portion 906, which can be insulated from other portions of the conductive interlayer. The serial connections between other cascaded strings can be formed similarly. Solar panel 900 can include multiple similarly connected larger strings, such as larger strings 912 and 914. To enhance the current output of solar panel 900, the multiple larger strings can be connected in parallel. Such parallel connections can also be achievable via the conductive interlayer in the backsheet. In the example shown in FIG. 9A, the positive polarities of all larger strings, including larger strings 912 and 914, can be coupled to portion 910, and the negative polarities of all larger strings can be coupled to portion 920. Portions 910 and 920 can be separated from each other to prevent shorting. On the other hand, the panel output can be obtained from the back side of the panel via contacts 922 and 924, which are coupled electrically to portions 910 and 920, respectively. More specifically, contacts 922 and 924 can be formed by creating vias at the bottom insulation layer of the backsheet and filling these vias with conductive paste. In addition, bypass diode 950 can also be coupled to contacts 922 and 924, which provide bypass protection to the entire panel. Shaded or partially shaded strings can be bypassed to prevent heating of the shaded strips. In the example shown in FIG. 9A, only one bypass diode is connected to the larger strings via the backsheet because the backsheet only provides access to ends of the larger strings. In practice, portions 910 and 920 can each be divided into smaller pieces to allow additional bypass diodes to be connected to a subset of cascaded strips in a larger string. For example, a bypass diode may be coupled to portion 906 and the back side of a strip in the middle of string 904 to protect a portion of string 904. One can see from FIG. 9A that connections to bypass diodes via the conductive interlayer can be much simpler compared to conventional approaches, thus making it possible to incorporate a relatively large number of bypass diodes in the panel. One extreme example is to couple each regularly sized photovoltaic structure (which can include multiple strips, such as three strips) with a bypass diode. In most cases, a number of strips connected in series (which can be a portion of a cascaded string) are coupled to a bypass diode. In FIG. 9A, vias that mechanically bond the strings and the backsheet are not shown.

In the example shown in FIG. 9A, gaps are formed in the conductive interlayer of the backsheet to electrically insulate different portions of the conductive interlayer, and vias are formed in the insulation layer to electrically couple the different portions of the conductive interlayer to corresponding electrodes of strings. These strategically located gaps and vias achieve the desired circuitry connection. More specifically, locations of the gaps and vias in the conductive interlayer are predetermined based on the layout of the panel. During the manufacturing process of the panel, the strips are first cascaded to form strings, then conductive paste is applied on the backsheet at locations of the vias, and at least the cascaded strings are carefully aligned to the backsheet to ensure that appropriate electrodes (busbars or contact pads) are in contact with the corresponding vias.

One drawback in the solution shown in FIG. 9A is that the large continuous conductive areas, such as portions 910 and 920, in the backsheet means that a relatively large amount of conductive material (e.g., Cu) is needed to manufacture the backsheet. To further reduce cost, instead of coupling the electrodes or contact pads to large sheets of conductive material to achieve electrical interconnections, some embodiments rely on smaller, continuous pieces of conductive material to achieve desired circuit connections. FIG. 9B shows the inter-string connections and the bypass protection strategy of a solar panel, according to an embodiment of the invention. In FIG. 9B, the panel layout is similar to what is shown in FIG. 9A, with solar panel 900 including a number of larger strings, such as larger strings 912 and 914. Each larger string includes a number of cascaded strings connected in series. For example, larger string 912 can include strings 902 and 904 connected in series, and two other strings, also connected in series. The inter-string serial connections are made through small and isolated pieces of conductive material within the conductive interlayer of the backsheet. For example, portion 906 connects strings 902 and 904 in series. On the other hand, instead of using larger sheets of conductive material, the parallel connections among the larger strings are achieved using smaller pieces 930 and 940. In some embodiments, conductive pieces 930 and 940 can be designed to be as small as possible, as long as they can achieve the desired electrical conductivity. Similarly, contacts 932 and 942, which are located at the back side of the panel, can provide panel output and enable coupling to bypass diode 950. Compared to FIG. 9A, the example shown in FIG. 9B relies on a backsheet that uses significantly less conductive material. In other words, the backsheet shown in FIG. 9B can be cheaper to make than the backsheet shown in FIG. 9A. Cheaper backsheets can lead to reduced overall cost for manufacturing solar panels. The positive and negative polarities shown in FIGS. 9A and 9B are for exemplary purposes only. In reality, the locations of the positive and negative polarities can be arbitrary, and can depend upon the layer structure and orientation of the cascaded cells.

FIG. 10 shows the flowchart of manufacturing a solar panel, according to an embodiment of the invention. The operation starts with obtaining a backsheet that can include the patterned conductive interlayer and a number of vias in the top and bottom insulation layers (operation 1002). The pattern of the conductive interlayer and locations of vias within the top (cell facing) insulation layer of the backsheet can be determined based on the panel layout, such as the interconnections of the cascaded strings and pre-designed bypass protection strategies. For example, if a portion of a string is designed to have bypass protection, one or more vias will be created at appropriate locations within the top insulation layer to facilitate coupling between the portion of the string and the bypass diode. Similarly, vias can be created at appropriate locations to facilitate serial or parallel connections among the cascaded strings. In addition, vias can also be created at locations where electrical connections are not needed to facilitate mechanical bonding. Portions of the conductive interlayer underneath such vias can be isolated from other portions. Locations of vias within the bottom (facing outside of the panel) insulation layer of the backsheet are determined based on the pattern of the conductive interlayer and the location of the junction box.

Subsequently, conductive paste can be applied to fill the vias within the top insulation layer of the backsheet (operation 1004), and the cascaded strings can be placed on the backsheet (operation 1006). The placement of the strings can be carefully controlled to ensure that the contact pads on the strings are placed above corresponding vias in the backsheet. Once the strings are placed, the system can apply heat to cure the paste to activate electrical conductivity (operation 1008). In some embodiments, a number of heaters can come in contact with photovoltaic structures at locations of the vias to cure the paste filled in the vias. The cured paste can provide mechanical bonding and electrical coupling between the strings and backsheet. Subsequently, the front glass cover can be applied to seal the strings within the glass cover and the backsheet (operation 1010). In some embodiments, the application of the glass cover is performed from beneath, and the backsheet and the strings are flipped over to allow the glass cover to be lifted from below to make soft contact with the strings.

Additional heat and pressure can be applied to laminate the strings between the glass cover and the backsheet (operation 1012), and the laminated module can be placed in a frame (operation 1014). A junction box can then be attached to provide panel output and bypass protection circuitry (operation 1016). In some embodiments, attaching the junction box can involve filling vias within the bottom insulation layer of the backsheet with conductive paste, connecting lead wires to such vias, and curing the paste.

In general, compared to conventional approaches for interconnecting strings and for coupling bypass diodes, embodiments of the invention provide a solution that achieves inter-string electrical coupling through a conductive interlayer within the backsheet of the solar panel, thus eliminating cumbersome wiring via metal wires (or tabs) at the panel surface. Placing all electrical connections within the backsheet can reduce shading, and the elimination of inter-string metal wires (or tabs) can prevent occurrences of thermal and mechanical stresses introduced by the wires. Moreover, having all contacts at one side of the strings can significantly simplify the manufacturing process by eliminating the need to flip over individual photovoltaic structures, as needed in the manufacturing of conventional solar panels. When strings are flipped, they can be flipped as a whole, and the mechanical bonding provided by a number of paste-filled vias situated between the contact pads and the conductive interlayer can ensure that the strings are securely bonded to the backsheet during the flipping process.

The foregoing descriptions of various embodiments have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the invention. 

What is claimed is:
 1. A solar panel, comprising: a cover; a backsheet comprising a first insulation layer, a second insulation layer, and a conductive interlayer positioned between the first insulation layer and the second insulation layer; and a plurality of solar cell strings positioned between the cover and the first insulation layer of the backsheet; wherein the first insulation layer comprises a plurality of vias, and wherein the conductive interlayer is patterned according to locations of the vias, thereby facilitating electrical interconnections among the solar cell strings.
 2. The solar panel of claim 1, wherein the first insulation layer comprises polyethylene terephthalate (PET), fluoropolymer, polyvinyl fluoride (PVF), polyamide, or any combination thereof; and wherein the conductive interlayer comprises Al, Cu, graphite, conductive polymer, or any combination thereof.
 3. The solar panel of claim 1, wherein a respective via is filled with a conductive paste to facilitate: electrical coupling between a contact pad located on a corresponding solar cell string and the conductive interlayer; and/or mechanical bonding between a contact pad located on a corresponding solar cell string and the conductive interlayer.
 4. The solar panel of claim 1, wherein a respective solar cell string comprises a plurality of cascaded photovoltaic structures.
 5. The solar panel of claim 1, further comprising a plurality of bypass diodes, wherein a respective bypass diode is coupled to a photovoltaic structure through the conductive interlayer.
 6. The solar panel of claim 1, wherein a conductive path between a first solar cell string and a second solar cell string comprises: a first contact pad of the first solar cell string; a first set of vias within the first insulation layer, wherein the first set of vias are filled with a conductive paste and are positioned beneath the first contact pad; a second contact pad of the second solar cell string; a second set of vias within the first insulation layer, wherein the second set of vias are filled with the conductive paste and are positioned beneath the second contact pad; and a continuous portion of the conductive interlayer that is in contact with both the first and second sets of vias.
 7. The solar panel of claim 1, wherein the second insulation layer comprises a plurality of vias filled with a conductive paste to electrically couple the interconnected solar cell strings to a junction box.
 8. A method for manufacturing a solar panel, comprising: obtaining a backsheet that comprises a first insulation layer, a second insulation layer, and a conductive interlayer positioned between the first insulation layer and the second insulation layer, wherein the first insulation layer comprises a plurality of vias, and wherein the conductive interlayer is patterned according to locations of the vias; overlaying a plurality of solar cell strings on the backsheet, wherein the first insulation layer faces the solar cell strings, and wherein the solar cell strings are overlaid in such a way that selected contact pads of the solar cell strings are positioned above the vias, thereby facilitating electrical interconnections among the solar cell strings; and laminating the solar cell strings between the backsheet and a glass cover.
 9. The method of claim 8, wherein the first insulation layer comprises polyethylene terephthalate (PET), fluoropolymer, polyvinyl fluoride (PVF), polyamide, or any combination thereof; and wherein the conductive interlayer comprises Al, Cu, graphite, conductive polymer, or any combination thereof.
 10. The method of claim 8, further comprising filling the vias with a conductive paste, wherein a respective via filled with the conductive paste is configured to facilitate: electrical coupling between a contact pad located on a corresponding solar cell string and the conductive interlayer; and/or mechanical bonding between a contact pad located on a corresponding solar cell string and the conductive interlayer.
 11. The method of claim 8, wherein a respective solar cell string comprises a plurality of cascaded photovoltaic structures.
 12. The method of claim 8, further comprising coupling a plurality of bypass diodes to the interconnected solar cell strings, wherein a respective bypass diode is coupled to a photovoltaic structure through the conductive interlayer.
 13. The method of claim 8, further comprising establishing a conductive path between a first solar cell string and a second solar cell string by curing a conductive paste that fills the vias, wherein the conductive path comprises: a first contact pad of the first solar cell string; a first set of vias within the first insulation layer, wherein the first set of vias are filled with the conductive paste and are positioned beneath the first contact pad; a second contact pad of the second solar cell string; a second set of vias within the first insulation layer, wherein the second set of vias are filled with the conductive paste and are positioned beneath the second contact pad; and a continuous portion of the conductive interlayer that is in contact with both the first and second sets of vias.
 14. The method of claim 8, further comprising filling vias included in the second insulation layer with a conductive paste to electrically couple the interconnected solar cell strings to a junction box.
 15. A photovoltaic structure encapsulation mechanism, comprising: a transparent cover; and a non-transparent cover comprising a first insulation layer, a second insulation layer, and a conductive interlayer positioned between the first insulation layer and the second insulation layer; wherein the first insulation layer comprises a plurality of through holes, and wherein the conductive interlayer is patterned according to locations of the through holes, thereby facilitating electrical interconnections among solar cell strings sandwiched between the transparent cover and the non-transparent cover.
 16. The photovoltaic structure encapsulation mechanism of claim 15, wherein the first insulation layer comprises polyethylene terephthalate (PET), fluoropolymer, polyvinyl fluoride (PVF), polyamide, or any combination thereof; and wherein the conductive interlayer comprises Al, Cu, graphite, conductive polymer, or any combination thereof.
 17. The photovoltaic structure encapsulation mechanism of claim 15, wherein a respective through hole is filled with a conductive paste.
 18. The photovoltaic structure encapsulation mechanism of claim 17, wherein the conductive paste comprises: a conductive metallic core surrounded by a resin; and/or a resin comprising a number of suspended conductive particles.
 19. The photovoltaic structure encapsulation mechanism of claim 17, wherein the through hole filled with the conductive paste facilitates: electrical coupling between a contact pad located on a corresponding solar cell string and the conductive interlayer; and/or mechanical bonding between a contact pad located on a corresponding solar cell string and the conductive interlayer.
 20. The photovoltaic structure encapsulation mechanism of claim 15, wherein the second insulation layer comprises a plurality of through holes filled with a conductive paste to electrically couple the interconnected solar cell strings to a junction box. 